1. Field of Invention
The invention relates to a package structure of an optical-electronic device and the method for making the same. In particular, the invention relates to a wafer level package structure of an optical-electronic device and the manufacturing method thereof.
2. Related Art
The optical-electronic device is the key component in a digital camera device. It converts received optical signals into electrical signals for generating digital pixel data. They are mainly used in various digital image electronics, such as security monitors, digital cameras, computer videoconference devices, mobile phones, PDA's, image phones, and fingerprint recognizers.
As digital image electronics become lighter, more compact and functional, there are higher demands in reducing the packaging cost, increasing the element density, and decreasing the element sizes. As the manufacturing technology improves, transistors become much smaller. Traditional packaging seems to waste space. The mini-packaging of optical-electronic devices nowadays mostly uses the chip on board (COB) packaging or the chip size packaging (CSP). The COB packaging directly packages the die on a printed circuit board (PCB). This packaging technology is actually a miniature surface mounting technology. Metal wires are used to connect I/O pads to the circuit on the PCB. The die is covered by filling with an adhesive agent. This method can effectively transfer the packaging and testing steps during the manufacturing process to the circuit board assembly stage. However, since the die is directly attached onto the circuit board for packaging, it is likely to pollute the lens set during the packaging process, resulting in a lower yield.
The CSP is a wafer level chip size packaging technology, according to which the wafer is first packaged and tested before being cut into individual chips. It does not need bonding and adhesive agent filling steps. The chip size after packaging is the same as the original die. Therefore, the wafer level chip size packaging technology not only keeps the original size of the packaged devices in order to satisfy the high-density integrated space requirement of mobile information products, it also shorten the circuit path on the chip. By directly connecting solder balls with the circuit board, the information transmission speed is highly increases, reducing the noise interference probability.
The integrated circuit (IC) device disclosed in the U.S. Pat. No. 6,646,289 is a CSP method. Several dies are first formed on a wafer (semiconductor substrate), followed by packaging each die. The packaging steps include forming circuits and at least one protection layer on the front surface of the wafer, forming solder pads on the back of the wafer for connecting to the circuits, and cutting the wafer into individual devices. Since the key step in the manufacturing process is to connect the solder pads on the back to the circuits on the front, it is necessary to etch at the scribe lines on the wafer to the protection layer, followed by depositing a conductive film at the etching place for connection to the circuits on the front surface.